Graft rejection of biological cells, organs, devices and the like that are placed into living organisms severely limits many medical treatments. For example, pancreatic transplantation, which is the only treatment of Type I diabetes that is capable of consistently inducing insulin independence and normalizing blood glucose is severely limited by graft rejection and the need for toxic immunosuppression.
One theory advanced to overcome the limitation caused by graft rejection is to place pancreatic islets in an immuno protected device that would allow the diffusion of insulin generated by the islet cells. Heretofore in the art, the term immunoisolation has been used to describe the state of being protected from immune rejection by enclosure within a membrane. It has been advanced that semipermeable membranes would be highly desirous for this task.
Semipermeable membranes are known. For example, Kennedy et al. in U.S. Pat. Nos. 4,942,204 and 5,073,381 teach amphiphilic networks that are employed as pharmaceutical carries capable of controlled drug release. More specifically, the amphiphilic networks are copolymeric compositions having hydrophobic and hydrophilic segments. Although these networks are synthesized for controlled drug release devices, implants for enzyme immobilization, artificial arteries, blood-contacting applications, and various implantable reservoirs for drugs and metabolites for veterinary and human applications, the amphiphilic networks taught therein are not synthesized to prevent the diffusion of molecules, and moreover, prevent the diffusion of molecules having a certain molecular weight while allowing the diffusion of molecules of a different molecular weight. In other words, a need still exists to synthesize and employ a semipermeable membrane to create an implantable device capable of immunoisolating cells.